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標題: | 利用自組裝方式合成鋰離子電池矽碳負極材料 Silicon-Graphite Anodes Enabled by Self-Assembly for Lithium Ion Batteries |
作者: | Shu-Jui Chang 張書睿 |
指導教授: | 吳乃立(Nae-Lih Wu) |
關鍵字: | 鋰離子電池,自組裝,矽碳負極,噴霧乾燥, Li-ion batteries,Self-assembly,Silicon-carbon composite,Spray drying, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 本研究以天然石墨以及奈米矽顆粒為原料,試圖以天然石墨粉體的加工及利用奈米矽顆粒原生帶有的電荷,以最簡單的方式且可大規模製造的方法合成出具有商業化潛力之鋰離子電池矽碳複合負極材料。最後,我們在成品上採用一些作法試圖提升材料的循環壽命及穩定性。 為了要大規模生產,實驗過程中使用了噴霧造粒技術及利用靜電吸附自組裝方式來減少材料合成的複雜流程。首先,我們想製造帶有正電荷的天然石墨顆粒,利用表面塗佈方法試圖使一種帶有正電荷的高分子Poly(diallyldimethylammonium chloride) (PDDA)附著於天然石墨的表面,但我們已知PDDA在水中溶解度很高,為了避免PDDA在水中與天然石墨分離,所以我們使用了Polyvinyl Alcohol (PVA)與一些交聯劑經過高溫交聯反應能夠成為難溶於水高分子膜的特性,將PDDA固定於天然石墨表面上。為了確認這一個步驟的可行性,我們先以小規模的實驗,在經過Zeta potential電量測量以確保此方法可行後,再使用噴霧乾燥方式來提高產量,而每一批次的產量能夠提升到50克以上。 而本實驗中的奈米矽顆粒來自於德國布倫瑞克工業大學(TU Braunschweig),粒徑大小大約為150奈米,而顆粒表面帶有負電荷,且在水中帶有相當多的負電電量。如此一來奈米矽顆粒可利用相異電荷與加工過後的石墨在水中進行靜電吸附,自然地相互吸引在一起,讓奈米矽顆粒可均勻地吸附於石墨表面,同時也利用奈米矽顆粒間的同性電荷解決顆粒容易聚集的問題。 最後一步的瀝青塗層,瀝青在經過高溫裂解之後會殘留有非常大量的碳,所生成的碳層故能夠將矽顆粒固定在石墨表面上,可以確保煅燒後奈米矽仍能保留在石墨表面不脫落,殘留的碳同時也能增加顆粒的導電度。我們透過各種表面分析技術,可以觀察到奈米矽顆粒均勻地披覆於石墨表面,且瀝青徒步在經過高溫裂解確實能於顆粒表面上產生均勻的碳層。 在研究的最後一部分中,我們嘗試引用高分子鍍膜技術以及實驗室其他成員研發之PVDF電極塗布技術試圖改進材料電性表現。本研究的做法有二: 一、將極片浸於PVDF溶液中並置於真空環境使高分子完全填入孔隙。 二、將粉體顆粒與PVDF直接均勻混合後,加熱使高分子熔化於粉體表面上。 這樣做的目的在於製造一層人造固體電解質介面膜Artificial-Solid Electrolyte Interphase (A-SEI),可以減少矽碳活物對電解液的直接接觸,減緩劇烈的SEI 生長,且在結構上對含矽負極產生穩固和保護效果,進而增強負極材料的性能以及長久電容量的穩定性。 In this study, natural graphite and nano-silicon particles (SiNPs) were used as raw materials. To synthesize lithium-ion battery Silicon-carbon composite anode materials which have great potentialities in the uncomplicated and large-scale manufacturing method. We used the processing of powder and the charges inherent in the particles. Finally, we tried some methods to improve the stability of the material. In order to manufacture in large-scale, spray drying and self-assembly methods were used in the experimental process to reduce the complicated procedure of material synthesis. First of all, we tried to coat a positively charged polymer, like Poly (diallyldimethylammonium chloride) (PDDA) on the surface of graphite using a surface coating method, but we know that PDDA is natural to soluble with water, so we used Polyvinyl Alcohol (PVA) and a cross-linking agent. Cross-linking reaction will happen after high-temperature heating, it can become a water-resistant polymer film, and can fix PDDA on the graphite surface. In order to confirm the feasibility of this step, we first carried out a small-scale experiment. After measuring the Zeta potential to ensure that the method is feasible, we use spray drying for this process, with a yield of at least 50 grams per batch. The SiNPs in this experiment comes from the Technical University of Braunschweig, Germany. The particle size is about 150 nanometers, and it can generate a negative charge in water. The use of natural charge can solve the problem of agglomeration, which is also a common problem that happened with nanoparticles. In addition, PDDA@NG and SiNPs with different charge can naturally attract to each other in the water, so that the SiNPs can be uniformly adsorbed on the graphite surface. The final step of pitch coating enables the fixation of SiNPs on the graphite surface, and a substantial amount of carbon remains after high-temperature cracking. At the same time, the carbon layer can improve the conductivity of the particles. Through surface analysis technology, we can observe that SiNPs cover the graphite surface uniformly, and pitch can also generate a uniform carbon layer on the surface of the particles. In the last part of the study, we tried to use the PVDF coating technology developed by other members of the laboratory to improve the performance of the material. The research has two approaches: 1. Immerse the electrode into the PVDF solution and place it in a vacuum environment so that the polymer fills the voids. 2. Mix the powder particles with PVDF directly and uniformly. Then let PVDF melt on the powder surface by heating. The purpose of these approaches is to manufacture a layer of Artificial-Solid Electrolyte Interphase (A-SEI), which can reduce the contact of silicon-carbon active materials to the electrolyte, suppress the violently growing of SEI, and improve the capacity and retention. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/15473 |
DOI: | 10.6342/NTU202001628 |
全文授權: | 未授權 |
顯示於系所單位: | 化學工程學系 |
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